That woman will try to find out what's in Molly Malone's wheelbarrow (9)
I believe the answer is:
shellfish
'find out what's in molly malone's wheelbarrow' is the definition.
I can't tell whether this definition defines the answer.
'that woman will try' is the wordplay.
'that woman will' becomes 'shell' (contraction of 'she will').
'try' becomes 'fish' (I can't explain this - if you can you should believe this answer much more).
'shell'+'fish'='SHELLFISH'
'to' is the link.
Can you help me to learn more?
(Other definitions for shellfish that I've seen before include "Oysters, crabs, shrimps etc" , "Crustaceans" , "paella ingredient" , "Lobsters, cockles, mussels etc" , "provider of pearls?" .)